Solid-fuel gas generators are often used in missiles and rockets to produce hot, high-pressure gas to use as propellant. In some systems, the hot gas is fed to a secondary combustor where it mixes within an in-flowing oxidant, such as air. The gas burns in the secondary combustor and is then exhausted from a thrust nozzle. In some other systems, a secondary combustor is not present; the gas generated by the solid-fuel gas generator is simply delivered to and exhausted from the thrust nozzle.
It is often necessary to vary a missile's attitude and speed during flight. For missiles that are powered by solid-fuel gas generators, this requires regulating the gas flow during flight, since the gas-generating reaction is uncontrolled. The gas flow can be regulated using a hot-gas control valve.
In some propulsion systems, the hot-gas control valve is positioned to regulate the flow of gas into the combustor. In some other systems, the control valve is positioned to regulate the flow of gas to the thrust nozzle. In yet some other systems, control valves regulate gas flow to both the combustor and the nozzle.
FIGS. 1A and 1B depict a simplified schematic of a conventional solid-fuel-sourced propulsion system that includes solid-fuel gas generator 99 for generating propulsion gas 100 and two-stage hot-gas control valve 108 for regulating the flow of gas 100 to thrust nozzle 102. A two-stage valve is often used for this service (as opposed to a single-stage valve) as a way to reduce valve-actuator power requirements or improve valve response time. FIG. 1A depicts two-stage valve 108 in a “closed” state, wherein gas 100 is prevented from entering mouth 104 of nozzle 102. FIG. 1B depicts valve 108 in an “open” state, wherein gas 100 is permitted to enter mouth 104 of nozzle 102.
Two-stage control valve 108 includes “first stage” or “pilot valve” 110 and “second stage” or “main-stage valve” 112. The structure of pilot valve 110 is not depicted in FIGS. 1A and 1B; pilot valve 110 is typically one of several known valve types, such as a flapper valve, spool valve or the like. In the illustration, second stage 112 is a linearly-acting, piston-in-bore arrangement.
Regardless of its particular configuration, pilot valve 110 actuates second stage 112 of the two-stage valve 108 depicted in FIGS. 1A and 1B. In the state depicted in FIG. 1A, pilot valve 110 causes piston 114 to move “upwards” in bore 116, sealing mouth 104 of nozzle 102. This prevents gas 100 in conduit 106 from entering nozzle 102. In the state depicted in FIG. 1B, pilot valve 110 causes piston 114 to move “downwards” in bore 116, such that mouth 104 of nozzle 102 is open. In this state, gas 100 flows into nozzle 102. Piston 114 can actuated pneumatically, electromechanically, or via other modalities.
As conventionally implemented, pilot valve 110 must overcome certain forces to operate. For example, if pilot valve 110 is a flapper valve, the valve element (i.e., the “flapper,”) must typically “lift” against a pressure load. And while some valves are statically pressure balanced, they are usually not dynamically pressure balanced. When used for aeronautical applications, such as in a missile, most conventional implementations of pilot valve 110 must also contend with g-forces.
Overcoming these loads necessitates an increase in the power required for actuation relative to what would otherwise be necessary. Consequently, it would be desirable to provide a valve (e.g., a pilot valve for a two-stage, hot-gas control valve, etc.) that is configured such that it does not lift against a pressure load, is substantially insensitive to g-loads, and is immune from pressure imbalances.